Saponin-digesting enzymes, genes thereof and soyasapogenol B mass production system

ABSTRACT

The present invention provides a protein having saponin-decomposing activity, more specifically a protein which can decompose a glycoside having soyasapogenol B as an aglycone to produce soyasapogenol B, a polynucleotide encoding such a protein, and a method of producing soyasapogenol B on a large scale using the same. A protein according to the present invention are concerned with (a), (b) or (c), namely (a) a protein comprising an amino acid sequence selected from the group consisting of the amino acid sequences shown in SEQ ID NOs: 2, 4, and 6; (b) a protein that has at least 50% homology to the protein comprising the amino acid sequence of the sequence described in (a) and having saponin-decomposing activity; or (c) a protein comprising a modified amino acid sequence of the sequence described in (a) that has one or more amino acid residues deleted, substituted, inserted, or added and having saponin-decomposing activity.

This application is a U.S. national stage of International Application No. PCT/JP02/05615 filed Jun. 6. 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel saponin-decomposing enzyme, a gene thereof, and a novel method for producing soyasapogenol B using them.

2. Background Art

Soyasapogenol B (12-oleanane-3,22,24-triol) is one of the aglycones of saponins contained in legumes and has been reported to have various physiological activities since early times. For example, platelet aggregation suppressing effect, anticomplementary activity, and preventive and therapeutic activity for nephritis, rheumatism, immune diseases such as systemic lupus erythematosus, autoimmune diseases or thrombosis have been reported (Chem. Pharm. Bull., 24, 121–129, 1976; Chem. Pharm. Bull., 30, 2294–2297, 1982; Kagaku to Seibutsu, 21, 224–232, 1983; Japanese Patent Application Laid-open No. 37749/1986). Further, growth-suppressing effect on cells derived from human colon cancer and human ovarian cancer has been reported (Japanese Patent Application Laid-open No. 37749/1986; Japanese Patent Application Laid-open No. 234396/1998).

Soyasapogenol B can be produced, for example, by chemically hydrolyzing sugar chains of saponins contained in soybean seeds as glycosides (soyasaponins I–V). However, this is not an effective production method because a considerable number of by-products may be produced depending on the conditions for acid hydrolysis. Further, soybean seeds are known also to contain saponins which have soyasapogenol A (soyasaponins A1–A6) or soyasapogenol E as an aglycone. Therefore, when soyasapogenol B is prepared from soybeans, the resulting preparation may easily contain soyasapogenol A and soyasapogenol E as impurities so that it is difficult to purify soyasapogenol B alone from such preparation. Further, since the saponin content of soybean seeds is generally as low as about 0.2% (Yakugaku Zasshi, 104, 162–168, 1984), there is a need for more efficient production.

As for methods of producing soyasapogenol B using microorganisms, a method with genus Streptomyces (Chem. Pharm. Bull. 32: 1287–1293, 1984) and a method with genus Penicillium (Japanese Patent Application Laid-open No. 234396/1998) is known. However, these methods of producing soyasapogenol B using microorganisms are poor in productivity and practicality.

Further, it has been reported that soyasapogenol B can be obtained as a by-product in a method in which an acid oligosaccharide having glucuronic acid as the reduced end is produced by hydrolyzing a glucuronide saponin using the enzyme (glucuronidase) produced by microorganisms that belong to genus Aspergillus or a culture containing this enzyme (Japanese Patent Publication No. 32714/1995). However, this method is primarily a method of producing acid oligosuccharides, and only a qualitative confirmation of soyasapogenol B is described in this report. Further, this report revealed the molecular weight of the enzyme having activity of interest but not the amino acid sequence thereof.

On the other hand, the search for microorganisms which efficiently produce soyasapogenol B by selectively hydrolyzing a glycoside having soyasapogenol B as an aglycone resulted in finding filamentous fungus strains that belong to genus Neocosmospora or genus Eupenicillium. It has been found that soyasapogenol B is produced and accumulated in a culture medium at a high concentration by culturing filamentous fungi, that belong to genus Neocosmospora or genus Eupenicillium, in a medium containing a saponin (a glycoside having soyasapogenol B as an aglycone) (see WO 01/81612).

Examples of such filamentous fungi include Neocosmospora vasinfecta var. vasinfecta PF1225 that belongs to genus Neocosmospora and Eupenicillium brefeldianum PF1226 that belongs to genus Eupenicillium (see WO 01/81612).

Soyasapogenol B of interest can be produced using such fungi as they are, depending on the amount of saponins added to the medium. However, the amount of saponins to be added to the medium is limited because of the surface-active property of saponins, which easily foam. Further, viscosity of the medium supplemented with saponins is expected to increase because of the surface-active property. Accordingly, in order to improve the yield in producing the target substance from the culture, the extraction process has to be repeated several times. Further, soybean extract, which is generally used as a natural resource to effectively supply saponins, usually contains components other than saponins, such as lipids, proteins and polysaccharides. Therefore, the possible amount of saponins to be added to a medium ultimately depends on the purity of the soybean extract, which does not necessarily assure efficient production.

There is a need to develop a method for the large scale production of soyasapogenol B by an enzyme reaction using a saponin-decomposing enzyme producing enzyme, in which soyasapogenol B is efficiently produced and a high yield is maintained independently of the saponin content in a soybean extract, contrary to conventional methods.

SUMMARY OF THE INVENTION

Recently, the present inventors succeeded in isolating and purifying a protein having saponin-decomposing activity from microorganisms having saponin-decomposing activity (occasionally called “saponin-decomposing enzyme” hereinafter) and in identifying a gene encoding this protein. Further, the present inventors were able to obtain a highly active saponin-decomposing enzyme by expressing the resulting gene in a heterologous host. Further, the present inventors were able to effectively produce soyasapogenol B by carrying out an enzyme reaction using the saponin-decomposing enzyme thus obtained. The present invention is based on these findings.

Accordingly, an objective of the present invention is to provide a protein having saponin-decomposing activity, more specifically a protein which can decompose a glycoside having soyasapogenol B as an aglycone to produce soyasapogenol B, a polynucleotide encoding such protein, and a method of producing soyasapogenol B on a large scale using the same.

A protein according to the present invention is selected from the group consisting of the followings:

(a) a protein comprising an amino acid sequence selected from the group consisting of the amino acid sequences shown in SEQ ID NOs: 2, 4, and 6;

(b) a protein that has at least 50% homology to the protein comprising the amino acid sequence of the sequence described in (a) and having saponin-decomposing activity; and

(c) a protein comprising a modified amino acid sequence of the sequence described in (a) that has one or more amino acid residues deleted, substituted, inserted, or added and having saponin-decomposing activity.

A polynucleotide according to the present invention is selected from the group consisting of the followings:

(i) a polynucleotide consisting of a DNA sequence selected from the group consisting of the DNA sequences of SEQ ID NOs: 1, 3, and 5;

(ii) a polynucleotide that has at least 70% homology to the polynucleotide consisting of the DNA sequence of (i) and encodes a protein having saponin-decomposing activity;

(iii) a polynucleotide consisting of a modified DNA sequence of the sequence described in (i) that has one or more bases deleted, substituted, inserted, or added and encodes a protein having saponin-decomposing activity; and

(iv) a polynucleotide that hybridizes with a polynucleotide comprising the DNA sequence described in (i) under stringent conditions and encodes a protein having saponin-decomposing activity.

A recombinant vector according to the present invention comprises a polynucleotide of the present invention.

Further, a host according to the present invention is a host transformed with the abovementioned recombinant vector.

A process for producing a protein of interest according to the present invention comprises culturing the abovementioned transformed host and collecting a protein having saponin-decomposing activity from the resulting culture.

According to the present invention, a highly active saponin-decomposing enzyme can be obtained. Further, by using this enzyme, soyasapogenol B can be obtained efficiently and on a large scale from saponin. According to this method, soyasapogenol B can be obtained independently of the saponin content of, for example, a soybean extract.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the construction and restriction map for plasmid pCB-SBe.

FIG. 2 shows the optimum pH for recombinant saponin-decomposing enzymes in Example 5. In the Figure, the wild-type SDN means the saponin-decomposing enzyme derived from Neocosmospora vasinfecta var. vasinfecta PF1225, and the recombinant SDN means the recombinant saponin-decomposing enzyme.

FIG. 3 shows the optimum temperature for recombinant saponin-decomposing enzymes in Example 5. In the Figure, the wild-type SDN means the saponin-decomposing enzyme derived from Neocosmospora vasinfecta var. vasinfecta PF1225, and the recombinant SDN means the recombinant saponin-decomposing enzyme.

FIG. 4 shows the construction and restriction map for plasmid pCB-SDAe.

FIG. 5 shows the optimum pH for recombinant saponin-decomposing enzymes in Example 8. In the Figure, the wild-type SDA means the saponin-decomposing enzyme derived from Aspergillus sp. PF1224, and the recombinant SDA means the recombinant saponin-decomposing enzyme.

FIG. 6 shows the optimum temperature for recombinant saponin-decomposing enzymes in Example 8. In the Figure, the wild-type SDA means the saponin-decomposing enzyme derived from Aspergillus sp. PF1224, and the recombinant SDA means the recombinant saponin-decomposing enzyme.

FIG. 7 shows the construction and restriction map for plasmid pCB-SDEs.

FIG. 8 shows the optimum pH for recombinant saponin-decomposing enzymes in Example 12. In the Figure, the wild-type SDE means the saponin-decomposing enzyme derived from Eupenicillium brefeldianum PF1226, and the recombinant SDN means the recombinant saponin-decomposing enzyme.

FIG. 9 shows the optimum temperature for recombinant saponin-decomposing enzymes in Example 12. In the Figure, the wild-type SDE means the saponin-decomposing enzyme derived from Eupenicillium brefeldianum PF1226, and the recombinant SDE means the recombinant saponin-decomposing enzyme.

FIG. 10 shows the result made a comparison with SDN, SDA and SDE by seaching their homology each other.

DETAILED DESCRIPTION OF THE INVENTION

Deposition of Microorganisms

The strain Neocosmospora vasinfecta var. vasinfecta PF1225 was deposited with the International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki, Japan 305-5466, dated Mar. 13, 2000 (original deposition date). The accession number is FERM BP-7475.

The strain Eupenicillium brefeldianum PF1226 was deposited with the International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki, Japan 305-5466, dated Mar. 13, 2000 (original deposition date). The accession number is FERM BP-7476.

The strain Aspergillus sp. PF1224 was deposited with the International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki, Japan 305–5466, dated May 24, 2001. The accession number is FERM BP-8004.

The strain Trichoderma viride MC300-1 was deposited with the International Patent Organism Depositary, National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki, Japan 305-5466, dated Sep. 9, 1996 (original deposition date). The accession number is FERM BP-6047.

Protein Having Saponin-Decomposing Activity

A saponin-decomposing enzyme isolated and purified from Neocosmospora vasinfecta var. vasinfecta PF1225 (FERM BP-7475) was revealed to be a novel enzyme system since it has no homology to any saponin-decomposing enzyme found to date and is different from glucronidase derived from a microorganism belonging to genus Aspergillus (a glycoprotein having a molecular weight of about 158,000 consisting of subunits each having a molecular weight of 35,000 and 45,000 described in Japanese Patent Publication No. 32714/1995), which decomposes glucronide saponin, in its subunit structure and molecular weight.

Further, the protein according to the present invention and glucronidase previously disclosed in the Patent Publication were studied for their identity and homology. Since the strain belonging to genus Aspergillus described in said Patent Publication was not readily available, another strain belonging to genus Aspergillus was used. The strain used was Aspergillus sp. PF1224, which was identified to be a filamentous fungus, Deuteromycetes, belonging to genus Aspergillus according to the microbial properties shown below.

(1) Colony Features

Colonies grow well on a Czapek's yeast extract agar medium at 25° C. attaining a diameter of 80 mm in 7 days. The colonies are yellow to yellowish green, woolly and rich in conidia and sclerotia. The reverse side becomes pale brown. Colonies grow well on a malt extract agar medium at 25° C. attaining a diameter of 80 mm in 7 days. The colonies are yellow to yellowish green, woolly and rich in conidia and sclerotia. The reverse side becomes ocherous. Colonies are slightly suppressed on either medium when cultured at 37° C.

(2) Morphological Features

Conidial heads are yellow to yellowish green and radiate to loose cylindrical. Conidiophores are rough and colorless and vesicles are rodlike to subglobose, bearing aspergilla on almost the entire surface. Monoseriate and biseriate aspergilla are mixed; they are generally biseriate. Metulae are 8–12×4–5 μm and phialides are 8–12×3–4 μm. Conidia are globose to subglobose, rough, and 4–6 μm in length.

The enzyme referred to as glucronidase was confirmed using Aspergillus sp. PF1224, which revealed that the saponin-decomposing enzyme isolated and purified from Aspergillus sp. PF1224 by the present inventors has a molecular weight of 90 kDa, an optimum pH of 5 to 6, and an optimum temperature of 45° C. to 50° C. (see Reference Example). Furthermore, it was revealed that the saponin-decomposing enzyme isolated and purified from Eupenicillium brefeldianum PF1226 has a molecular weight of 90 kDa, an optimum pH of 5 to 6, and an optimum temperature of 40° C. to 45° C.

The protein of the present invention and the glucuronidase described in the abovementioned Patent Publication were compared for their molecular weight and subunit configuration since information such as an amino acid sequence of glucronidase was not disclosed in this Patent Publication to compare homology of the amino acid sequence or the like. Results showed that the protein according to present invention is a protein different from the glucronidase described in the Patent Publication.

As mentioned above, the present invention provides a protein selected from the group consisting of:

(a) a protein comprising an amino acid sequence selected from the group consisting of the amino acid sequences shown in SEQ ID NOs: 2, 4, and 6;

(b) a protein that has at least 50% homology to the protein comprising the amino acid sequence of the sequence described in (a) and having saponin-decomposing activity; and

(c) a protein comprising a modified amino acid sequence of the sequence described in (a) that has one or more amino acid residues deleted, substituted, inserted, or added and having saponin-decomposing activity.

Namely, a protein according to the present invention comprises an amino acid sequence which is identical or substantially identical to the amino acid sequence shown in SEQ ID NO: 2, 4, or 6.

An amino acid sequence that is substantially identical to the amino acid sequence shown in SEQ ID NO: 2, 4, or 6 herein means an amino acid that is typically more than 50%, preferably more than 70%, more preferably more than 80%, further preferably more than 90%, furthermore preferably more than 95%, or most preferably more than 98% homologous to any one of the amino acid sequences shown in these SEQ ID NOs.

Further, these figures for homology shown in the present specification can be any figures calculated using a homology search program known to the skilled in the art. For example, figures can be readily calculated using default parameters in FASTA, BLAST, or the like.

For example, when the figures for homology has been calucutated using default parameters in the homology search program Genetyx (manufactured by Genetyx Co.), the figure for homology between SDN and SDA is 51%, that between SDA and SDE is 52%, and that between SDE and SDN is 51%.

Further, a protein comprising an amino acid sequence that is substantially identical to the amino acid sequence shown in SEQ ID NO: 2, 4, or 6 means a protein comprising a modified amino acid sequence that has one or more amino acid residues deleted, substituted, inserted, or added and having saponin-decomposing activity.

The number of amino acid residues that can be deleted, substituted, inserted, or added is preferably 1 to 50, more preferably 1 to 30, further preferably 1 to 10, furthermore preferably 1 to 5, and most preferably 1 to 2.

In a more preferred embodiment of the invention, the protein described in (b) above is a protein comprising a modified amino acid sequence that has one or more conservatively substituted amino acid residues in the amino acid sequence (a) above and having saponin-decomposing activity.

The expression “conservatively substituted” herein means that one or more amino acid residues are substituted with other amino acid residues which are chemically homologous not to substantially alter the protein activity. For example, a hydrophobic residue is substituted with another hydrophobic residue or a polar residue is substituted with another polar residue having the same electric charge. Functionally homologous amino acids of different types, which can be conservatively substituted in this way, are known to the skilled in the art. Examples of such amino acids include non-polar (hydrophobic) amino acids such as alanine, valine, isoleucine, leucine, proline, tryptophan, phenyalanine, and methionine; polar (neutral) amino acids such as glycine, serine, threonine, tyrosine, glutamine, asparagine, and cysteine; positively charged (basic) amino acids such as arginine, histidine, and lysine; and further, negatively charged (acidic) amino acids such as aspartic acid, and glutamic acid.

In the present invention, the term “protein having saponin-decomposing activity” means a protein that is verified to have an activity to decompose saponin. For example it means a protein which is verified to have saponin-decomposing activity when measured under the same conditions as described in Example 5. This protein can be isolated and purified from “organisms having saponin-decomposing activity” described below.

A protein according to the present invention can be obtained, for example, as follows.

An organisms having saponin-decomposing activity is cultured and a protein having saponin-decomposing activity is isolated and purified from the resulting culture using the saponin-decomposing activity as an index. The amino acid sequence of the protein thus purified is analyzed, an oligonucleotide encoding this sequence is synthesized, and the PCR (polymerase chain reaction) is carried out using DNA of said organism as a template to synthesize a long probe. A DNA sequence of the translation region of the saponin-decomposing enzyme gene is analyzed by the inverse PCR or the RACE (rapid amplification of cDNA ends) method using this probe. The translation region of the saponin-decomposing enzyme thus obtained is linked to a regulatory sequence which functions in a host to be used for expression to obtain an expression vector. This expression vector is used to transform the host, the resulting transformant is cultured, and thus a saponin-decomposing enzyme can be obtained.

An “organism having saponin-decomposing activity” herein can be any organism having saponin-decomposing activity and is not particularly limited and includes microorganisms and plants. Examples of such microorganism include filamentous fungi that belong to genus Neocosmospora, genus Aspergillus, and genus Eupenicillium. These fungi are used in manufacturing soy sauce and soybean paste by fermentation and known to have saponin-decomposing activity. Further, said microorganisms include actinomycetes and bacteria since some of them may also have saponin-decomposing activity. Said plants include plant itself, plant cells, callus or culture cells derived from leguminous plants since some saponin glycotransferase of such plants may catalyze reverse reaction.

In a preferred embodiment of the present invention, a protein or a polynucleotide according to the present invention is derived from a microorganism, more preferably a microorganism belonging to filamentous fungus. A microorganism belonging to such filamentous fungus is preferably filamentous fungus belonging to genus Neocosmospora, genus Aspergillus, or genus Eupenicillium.

Examples of filamentous fungi that belong to genus Neocosmospora include Neocosmospora vasinfecta var. vasinfecta PF1225 (accession number: FERM BP-7475) and mutants thereof. Examples of filamentous fungi that belong to genus Aspergillus include Aspergillus sp. PF1224 (accession number: FERM BP-8004) and mutants thereof. Examples of filamentous fungi that belong to genus Eupenicillium include Eupenicillium brefeldianum PF1226 (accession number: FERM BP-7476) and mutants thereof.

Polynucleotide

The present invention provides a polynucleotide which encodes a protein of the present invention.

A polynucleotide according to the present invention is typically a polynucleotide selected from the group consisting of (i) to (iv) described above.

Namely, according to one embodiment of the present invention, the polynucleotide comprises a DNA sequence selected from the group consisting of the DNA sequences shown in SEQ ID NOs: 1, 3, and 5.

According to another embodiment of the present invention, the polynucleotide comprises a DNA sequence having at least 70% homology to the polynucleotide comprising the DNA sequence shown in SEQ ID NO: 1, 3, or 5 and encodes a protein having saponin-decomposing activity. The homology to the polynucleotide comprising the DNA sequence shown in SEQ ID NO: 1, 3, or 5 is preferably more than 80%, more preferably more than 90%, furthermore preferably more than 95%, or most preferably more than 98%.

Further, figures for homology shown in the present specification can be any figures calculated using a homology search program known to the skilled in the art. For example, figures can be readily calculated using default parameters in FASTA, BLAST, or the like.

According to another embodiment of the present invention, the polynucleotide comprises a DNA sequence having one or more bases deleted, substituted, inserted, or added in the DNA sequence shown in SEQ ID NO: 1, 3, or 5 and encodes a protein having saponin-decomposing activity.

Here, the number of amino acid residues that can be deleted, substituted, inserted, or added is preferably 1 to 50, more preferably 1 to 30, further preferably 1 to 10, furthermore preferably 1 to 5, and most preferably 1 to 2.

According to still another embodiment of the present invention, the polynucleotide hybridizes with a polynucleotide comprising the DNA sequence shown in SEQ ID NO: 1, 3, or 5 under stringent conditions and encodes a protein having saponin-decomposing activity. Further, according to the present invention, the polynucleotide also implies a polynucleotide which is complementary to a polynucleotide encoding a protein having saponin-decomposing activity.

The term “stringent conditions” herein means controlled conditions under which a probe comprising a DNA sequence partly or entirely encoding an amino acid sequence of a protein according to the present invention hybridized with a gene encoding a corresponding homologue while this probe does not hybridize with glucronidase having a molecular weight described in Japanese Patent Publication No. 32714/1995. More specifically, for example, according to the method of ECL Direct DNA/RNA Labeling Detection System (Amersham) using the whole length of polynucleotide encoding the standardized amino acid sequence shown in SEQ ID NO: 1, 3, or 5 as a probe, pre-hybridization is first carried out for 1 hour (42° C.), after which said probe is added, hybridization (42° C.) is carried out for 15 hours, and then washing process is carried out first with a 0.5×SSC solution (SSC: 15 mM trisodium citrate, 150 mM sodium chloride) supplemented with 0.4% SDS and 6 M urea twice at 42° C. for 20 minutes and then with a 5×SSC solution twice at room temperature (about 25° C.) for 10 minutes.

Recombinant Vector

The present invention provides a recombinant vector comprising the abovementioned polynucleotide.

The procedure and method for constructing a recombinant vector according to the present invention can be any of those commonly used in the field of genetic engineering.

Examples of the expression vector as used herein include vectors which can be incorporated into a host chromosome DNA and vectors having a self-replicable autonomous replication sequence which can be present as a plasmid in a host cell, for example, pUC vectors (e.g., pUC18 and pUC118), pBluescript vectors (e.g., pBluescript II KS+), and plasmids such as pBR322 plasmid. One or more of copies of the gene can be present in a host cell.

A regulatory sequence for the recombinant vector can be any regulatory sequence which can function in a host and is not particularly limited. For example, a promoter, a terminator, and the like can be used. Such a regulatory sequence can be ligated to a gene encoding a protein having saponin-decomposing activity for the gene expression.

The ligation to a regulatory sequence can be carried out, for example, according to an ordinary method by inserting a translation region of a gene encoding a protein of interest (gene of interest) downstream of a promoter in the right direction. In this case, the protein can be expressed as a fusion protein by ligating the gene of interest to a foreign gene encoding a translation region of another protein.

The expressed protein having saponin-decomposing activity or the expressed fused protein having said activity can be produced in a host cell used for expression or released into a medium.

For example, a saponin-decomposing enzyme derived from Neocosmospora vasinfecta var. vasinfecta PF1225 (FERM BP-7475) was revealed to have a signal peptide sequence of 26 amino acid residues at the N-terminal side according to the DNA sequence analysis and N-terminal amino acid sequence analysis (see Example). Similarly, a saponin-decomposing enzyme derived from Aspergillus sp. PF1224 and a saponin-decomposing enzyme derived from Eupenicillium brefeldianum PF1226 were revealed to have signal peptide sequences of 28 amino acid residues and 17 amino acid residues at the N-terminal side, respectively.

Accordingly, for example, when filamentous fungi such as those belonging to genus Trichoderma and genus Aspergillus are used as a host, the protein can be released into a medium by utilizing a signal sequence included in this sequence.

Further, the saponin-decomposing enzyme derived from Neocosmospora vasinfecta var. vasinfecta PF1225 having a molecular weight of about 77 kDa is inferred to be glycoproteins from a molecular weight of about 68 kDa estimated from a deduced amino acid composition and a molecular weight of about 68 kDa of a protein expressed in strains of Escherichia coli and Trichoderma viride. Similarly, the saponin-decomposing enzyme derived from Aspergillus sp. PF1224 having a molecular weight of about 90 kDa is inferred to be glycoproteins from a molecular weight of about 65 kDa estimated from a deduced amino acid composition and a molecular weight of about 80 kDa of a protein expressed in strains of Trichoderma viride. Further, the saponin-decomposing enzyme derived from Eupenicillium brefeldianum PF1226 having a molecular weight of about 90 kDa is inferred to be glycoproteins from a molecular weight of about 65 kDa estimated from a deduced amino acid composition.

These sugar chain are presumed not to have great influence on the expression of activity. However, various modification after translation, such as addition of various sugar chains, can be carried out anticipating effective changes in heat resistance, optimum pH, stability during storage, or the like.

A recombinant vector according to the present invention can be constructed by further ligating a selective marker gene such as a drug resistance gene and/or a gene complementing a nutritional requirement.

A gene marker can be appropriately selected depending on the technique for selecting a transformant. For example, a gene encoding drug resistance or a gene complementing a nutritional requirement can be used. Examples of the drug resistance gene include genes conferring resistance to destomycin, benomyl, oligomycin, hygromycin, G418, pleomycin, bialaphos, blastcidin S, phleomycin, phosphinothricin, ampicillin, streptomycin, and kanamycin. Examples of the gene complementing a nutritional requirement include amdS, prG, argB, trpC, niaD, TRP1, LEU2, and URA3. Further, a gene marker can be a gene complementing a nutrient requirement indigenous to a host to be used for expression in systems for synthesizing various amino acids, vitamins, nucleic acids, or the like, or a gene complementing a nutrient requirement that is rendered by various mutagenic treatments.

Production of Transformant and Protein of Interest

The present invention provides a host transformed with the abovementioned recombinant vector.

A host to be used in the present invention is not particularly restricted and any organism which can properly transcript and translate a gene encoding a protein having saponin-decomposing activity can be used. Examples of the host include bacteria such as Escherichia coli and Bacillus spp., actinomycetes, yeasts, filamentous fungi such as Trichoderma spp. and mutants thereof.

A recombinant vector for the gene expression can be introduced into a host by an ordinary method. Examples of the method for the introduction include the electroporation method, the polyethylene glycol method, the aglobacterium method, the lithium method, and the calcium chloride method. A method effective to each host cell can be selected.

A transformant (transformed host cell) can be cultured according to an ordinary method by appropriately selecting a medium, culture conditions and the like.

Conventional components can be used in a medium. As a carbon source, glucose, sucrose, cellulose, starch syrup, dextrin, starch, glycerol, molasses, animal and vegetable oils, and the like can be used. As a nitrogen source, soybean powder, wheat germ, cornsteep liquor, cotton seed lees, bouillon, peptone, yeast extract, ammonium sulfate, potassium nitrate, urea, and the like can be used. If necessary, sodium, potassium, calcium, magnesium, cobalt, chlorine, phosphoric acid, sulfuric acid, and other inorganic salts that can produce ions, such as potassium chloride, magnesium sulfate, monopotassium phosphate, zinc sulfate, manganese sulfate, and copper sulfate, can be effectively added. If necessary, various vitamins, amino acids, trace nutrients such as nucleotides, and selective drugs such as antibiotics can be added. Further, organic and inorganic substances to promote the growth of transformants and enhance the expression of an introduced gene can be appropriately added.

Cultivation can be carried out in a medium selectively containing these components.

For example, in a liquid medium, the cultivation can be carried out using a culture method under an aerobic condition, a shaking culture method, an agitation culture method with aeration, a submerged culture method or the like. The pH of the medium is, for example, about 5 to 8. The cultivation can be carried out at a normal temperature, such as 14° C. to 40° C., preferably 26° C. to 37° C., for about 1 to 25 days.

In a method of producing a protein of interest according to the present invention, a gene expression product, namely the protein of interest having saponin-decomposing activity, can be obtained from the culture of transformed cells. The protein of interest can be obtained from the culture according to an ordinary method. For example, steps of the extraction from the culture (e.g., by mashing, and crushing under pressure), the recovery (e.g., by filtration and centrifugation), and/or the purification (e.g., by salting out and solvent precipitation) can be appropriately combined. Furthermore, in these steps, a protease inhibitor, such as phenylmethylsulfonyl fluoride (PMSF), benzamidine and leupeptin, can be added if necessary.

According to another embodiment of the present invention, it is also possible to express a gene encoding a protein having saponin-decomposing activity in a plant which produces saponins, such as plants of soybean, kidney bean, cowpea, pea, peanut, and broad bean, and alfalfa to generate a plant body containing soyasapogenol B, from which soyasapogenol B is directly obtained. In this case, actin, ubiquitin, cauliflower mosaic virus 35S promoter, or the like, or a regulatory sequence of a gene specifically expressed at a part, such as the seed, can be used.

A gene encoding a protein having saponin-decomposing activity is properly linked to such a regulatory sequence and further, a drug resistance gene conferring resistance to bialaphos, kanamycin, blastcidin S, or the like is linked if necessary. The resultant product can be introduced into a plant cell, for example, by a direct introduction method such as the particle-gun method, the PEG method, the electroporation method, and the microinjection method, or by an indirect introduction method using Ti plasmid vector of aglobacterium to generate a transformed plant cell. Introduction of the gene into a plant cell or plant body can be carried out according the method of Vaeck M. et al (Nature, 328, 33–37, 1987).

The plant cell thus transformed can be redifferentiated by the method known to the skilled in the art into a complete body of a transformed plant. Further, the transformed plant is cultivated and the resultant whole plants and/or organs, such as seeds, in which a gene encoding a protein having saponin-decomposing activity is expressed are harvested, from which soyasapogenol B can be obtained using a method suitable for its property, such as the solvent extraction method.

Production of Soyasapogenol B

Another embodiment of the present invention provides a method of producing soyasapogenol B which comprises decomposing a glycoside having soyasapogenol B as an aglycone using a culture containing a protein having saponin-decomposing activity which can be obtained from the abovementioned transformed host.

Further, still another embodiment of the present invention provides a method of producing soyasapogenol B which comprises decomposing a glycoside having soyasapogenol B as an aglycone using at least one kind of protein selected from the group consisting of the abovementioned protein and the protein which can be obtained from the abovementioned transformed host.

Examples of the “glycoside having soyasapogenol B as an aglycone” include soyasaponins I, II, III, IV, and V, azukisaponins II and V, astragaloside VIII, and sophoraflavoside I, which are primarily found in leguminous plants.

Examples of the substance containing a glycoside having soyasapogenol B as an aglycone include a substance extracted from soybeans or defatted soybeans (soybean cake) with hot water, alcohol or alcohol hydrate, or preferably a substance from which impurities such as proteins, sugars and lipids are removed by an ordinary method.

According to the present invention, soyasapogenol B can be obtained by allowing a culture containing a protein having saponin-decomposing activity, a protein according to the present invention or a protein obtained from a host according to the present invention to act on a substance containing a glycoside having soyasapogenol B as an aglycone and/or said glycoside.

More specifically, for example, about 1% to 10% by weight saponin (Koshiro Seiyaku) is dissolved in water or a buffer solution, such as an acetate buffer or a phosphate buffer, to which saponin-decomposing enzyme is added. The reaction is carried out at an appropriate temperature, for example 20° C. to 50° C., after which the resulting reaction solution is extracted with an organic solvent such as ethyl acetate to obtain soyasapogenol B.

EXAMPLES

The present invention is further illustrated by the following examples that are not intended as a limitation of the invention.

Reference Example 1 Confirmation of Aspergillus Saponin-Decomposing Enzyme

A PDA slant (about 1 cm²) of Aspergillus sp. PF1224 (PERM BP-8004) was inoculated into 100 ml of a TS medium (2.0% soluble starch, 1.0% glucose, 0.5% polypeptone, 0.6% wheat germ, 0.3% yeast extract, 0.2% soybean grounds, and 0.2% calcium carbonate (pH 7.0 before sterilization)) dispensed into a 500-ml Erlenmeyer flask. Incubation was then carried out at 25° C. for 3 days with shaking. The resulting culture (4 ml) was inoculated into 100 ml of an MY medium (4% malt extract, 2.0% yeast extract, 0.2% potassium dihydrogenphosphate, 0.2% ammonium sulfate, 0.03% magnesium sulfate heptahydrate, 0.03% calcium chloride dihydrate (pH 7.0)) supplemented with 4.0% soybean saponin (Koshiro Seiyaku) dispensed into a 500-ml Erlenmeyer flask and incubation was then carried out for 3 days with shaking.

Saponin-decomposing activity shown in Test Example 1 was used as an index in the purification of saponin-decomposing enzyme derived from Aspergillus hereinafter.

The resulting culture (about 800 ml) was filtered with a glass filter (G3) and then centrifuged (8,000 rpm, 30 minutes) to remove cell debris. Ammonium sulfate (294 g) was added to about 570 ml of the supernatant thus obtained and the resulting precipitate was recovered by centrifugation (8,000 rpm, 30 minutes). This precipitate was dissolved in about 120 ml of a buffer solution A (0.1 M sodium acetate buffer, 1 M ammonium sulfate (pH 5.8)) and the resulting solution was subjected to hydrophobic chromatography using Butyl Toyopearl 650S (26 mm i.d.×330 mm) (Tosoh Co.). Elution was carried out with a concentration gradient from a buffer solution B (0.1 M sodium phosphate buffer-1 M ammonium sulfate (pH 5.8)) to 0.1 M sodium phosphate buffer (pH 5.8) and an unadsorbed fraction and a fraction eluted with an ammonium sulfate at a concentration from 1 M to 0.5 M were recovered.

Each of the recovered fractions was concentrated using Pellicon XL (cut-off molecular weight: 10,000) (Millipore), after which 1 M Tris-HCl buffer and ammonium sulfate were added to the concentrate so as to make their concentration the same as in a buffer solution C (50 mM Tris-HCl buffer, 1 M ammonium sulfate (pH 7.5)) and the resulting solution was subjected to hydrophobic chromatography using 6 ml of Resource PHE (Amersham Biosciences). Elution was carried out with a concentration gradient from the buffer solution C to the 50 mM Tris-HCl buffer solution (pH 7.5) and an unadsorbed fraction was recovered.

The fraction thus obtained was concentrated using Ultrafree 15 (cut-off molecular weight: 5,000) (Millipore) and then subjected to gel filtration chromatography using Superdex 200 pg (16 mm i.d.×600 mm) (Amersham Biosciences). Elution was carried out with a buffer solution D (25 mM sodium phosphate buffer, 0.15 M sodium chloride (pH 5.8)) and a fraction of a cut-off molecular weight of about 90 kDa was recovered.

SDS-PAGE was carried out with this fraction and a single band with an estimated molecular weight of about 90 kDa was observed.

Test Example 1 Measurement of Saponin-Decomposing Activity

An enzyme solution containing an enzyme of interest was desalted using a PD-10 column (Amersham Biosciences), after which an equal volume of 2% saponin solution was mixed and reaction was carried out at 37° C. for about 16 hours. The resulting reaction solution was extracted with an equal volume of ethyl acetate and the resulting extract was developed using TLC (solvent system used: chloroform:methanol=95:5). Utilizing color reaction of vanillin-sulfuric acid, soyasapogenol B having an Rf value of 0.35 was detected to measure enzyme activity of the enzyme solution of interest.

Test Example 2 Quantitative Analysis of Saponin-Decomposing Activity

A diluted enzyme solution was added to 50 μl of a 2% saponin solution to make a total volume of 100 μl and the resulting admixture was reacted for 30 minutes. Next, the resulting reaction solution was extracted with an equal volume of ethyl acetate and a 50 μl portion of the extract was diluted with 450 μl of mobile phase. A 10 μl portion of the dilution was subjected to high performance liquid chromatography under the following conditions and a peak height at a retention time of about 7.5 minutes was measured. By comparing this height with that of authentic soyasapogenol B, saponin-decomposing activity of this enzyme was quantitatively evaluated.

Column: Inertsil ODS-2, 5 μm (4.6 mm i.d×250 mm)

Column temperature: 40° C.

Mobile phase: acetonitrile:methanol:water=50:35:15

Mobile phase flow rate: 0.8 ml/min

Example 1 Isolation and Purification of Saponin-Decomposing Enzyme Derived from Genus Neocosmospora (SDN)

A PDA slant (about 1 cm²) of Neocosmospora vasinfecta var. vasinfecta PF1225 (FERM BP-7475) was inoculated into 100 ml of a TS medium dispensed into a 500-ml Erlenmeyer flask. Incubation was carried out at 25° C. for 3 days with shaking. The resulting culture (4 ml) was inoculated into 100 ml of an MY medium supplemented with 4.0% soybean saponin (Koshiro Seiyaku) dispensed into a 500-ml Erlenmeyer flask and then incubation was carried out for 3 days with shaking.

Saponin-decomposing activity shown in Test Example 1 was used as an index in the purification of saponin-decomposing enzyme derived from genus Neocosmospora hereinafter.

The resulting culture (about 800 ml) was diluted with about 2 times volume of water and then centrifuged (8,000 rpm, 30 minutes) to remove cells. Ammonium sulfate (171 g) was added to the supernatant and the resulting precipitate was removed by centrifugation (8,000 rpm, 30 minutes). Further ammonium sulfate (5.73 g) was added to the resulting supernatant and the resulting precipitate was recovered by centrifugation (8,000 rpm, 30 minutes) and dissolved in 70 ml of a buffer solution C. The resulting solution was subjected to hydrophobic chromatography using Butyl Toyopearl 650S (26 mm i.d.×110 mm) (Tosoh Co.). Elution was carried out with a concentration gradient from a buffer solution C to 50 mM Tris-HCl buffer (pH 7.5) and an unadsorbed fraction was recovered.

Ammonium sulfate (about 239 g) was added to about 500 ml of this fraction and the resulting precipitate was recovered by centrifugation. The recovered precipitate was then dissolved in 4 ml of a buffer solution B and the resulting solution was subjected to hydrophobic chromatography using Phenyl Sepharose FF (16 mm i.d.×100 mm) (Amersham Biosciences). Elution was carried out with a concentration gradient from a buffer solution B to a 0.1 M sodium phosphate buffer solution (pH 5.8) and a fraction at an ammonium sulfate concentration of about 0.4 M was recovered.

The fraction thus recovered was subjected to gel filtration chromatography using Superdex 200 pg (16 mm i.d.×600 mm) (Amersham Biosciences). Elution was carried out with a buffer solution E (50 mM Tris-HCl buffer, 0.15 M sodium chloride (pH 7.5)) and a fraction of a cut-off molecular weight of about 76,000 was recovered.

SDS-PAGE was carried out with this fraction and a single band of an estimated molecular weight of about 77 kDa was observed.

Example 2 Amino Acid Sequence Analysis of Saponin-Decomposing Enzyme (SDN)

2a) Amino Acid Sequence of the N-Terminal Side

The fraction prepared as in Example 1 was subjected to SDS-PAGE and blotted onto a PVDF membrane (Immobilon-PSQ) (Millipore), after which the membrane was washed and dried in air. This was subjected to a protein sequencer model 492 (Applied Biosystems) to analyze the amino acid sequence.

The amino acid sequence obtained by the analysis was as follows:

N-terminal amino acid sequence: ASPPASVPNNPSSEEITLQ (SEQ ID NO: 7)

2b) Analysis of Inner Amino Acid Sequence (Peptide Mapping)

The fraction prepared in Example 1 was subjected to SDS-PAGE and the resultant proteins were stained using Coomassie Brilliant Blue R250. A single band stained at an estimated molecular weight of about 77 kDa was excised and destained using a 0.2 M ammonium bicarbonate buffer solution (pH 8.0) in 50% acetonitrile and dried at room temperature for about 2 hours in air.

Next, this gel strip was immersed in a 0.2 M ammonium bicarbonate buffer solution (pH 8.0) containing 0.02% Tween 20, after which trypsin (Promega) was added and reaction was carried out at 37° C. for 2 days. After the reaction, the supernatant was recovered and the gel strip was further washed 3 times with 60% acetonitrile and 0.1% trifluoracetic acid. The resulting washings and the reaction supernatant were combined, concentrated and subjected to a Model 172μ preparative HPLC system (Applied Biosystems) (RP-300 Aquiapore C18, 220×2.1 mm, with a concentration gradient from 0.1% trifluoracetic acid-35% acetonitrile to 0.085% trifluoracetic acid-35% acetonitrile). The following 5 polypeptides were fractionated.

Trp26.8: LVFNPSPK (SEQ ID NO: 8) Trp27.59: WNVAADGSGPSGEIR (SEQ ID NO: 9) Trp32.07: VTILHNPEGVAPITAK (SEQ ID NO: 10) Trp39.43: EHSDTIPWGVPYVPGSQ (SEQ ID NO: 11) Trp41.3: LTDYSFDWYSDIR (SEQ ID NO: 12)

Example 3 Cloning and Sequence Analysis of Saponin-Decomposing Enzyme (SDN)

3a) Preparation of Long Probe Using PCR

A genomic DNA was prepared from cultured cells of Neocosmospora vasinfecta var. vasinfecta PF1225 (FERM BP-7475) to be used as a template for PCR.

The genomic DNA was isolated according to the method of Horiuchi et al. (J. Bacteriol., 170, 272–278, 1988). First, cells cultured in a TS medium were recovered by centrifugation (7,500 rpm, 10 minutes). The cells thus obtained were lyophilized, suspended in a TE solution (10 mM Tris-HCl buffer, 1 mM EDTA (pH 8.0)) and then treated in a 3% SDS solution at 60° C. for 30 minutes. Then TE-saturated phenol extraction was carried out to remove cell debris.

The extract was precipitated with ethanol and treated with Ribonuclease A (Nippon Gene) and Proteinase K (Wako Pure Chemical Industries, Ltd.), and the nucleic acid was then precipitated with 12% polyethylene glycol 6000. The precipitate was subjected to TE-saturated phenol extraction and ethanol precipitation, and the resulting precipitate was dissolved in a TE solution to obtain the genomic DNA.

Based on the peptide sequences obtained in Example 2, the following oligonucleotides encoding these sequences were synthesized and used as primers for PCR:

Primer N1: CCIGCITCNGTNCCNAA (SEQ ID NO: 13) Primer N2: CCIGCIAGYGTNCCNAA (SEQ ID NO: 14) Primer 2A: CCRTCIGCNGCNACRTT (SEQ ID NO: 15) Primer 3A: CCCCAIGGDATNGTRTC (SEQ ID NO: 16) Primer 4A: ACICCYTCNGGRTTRTG (SEQ ID NO: 17)

The PCR was carried out using Takara Taq (Takara Shuzo Co., Ltd.). The fragments were amplified by repeating 10 cycles of 30 seconds at 94° C., 30 seconds at 45° C., and 3 minutes at 55° C., after heat denaturation at 94° C. for 1 minute, followed by 20 cycles of 30 seconds at 94° C., 30 seconds at 47° C., and 3 minutes at 60° C. As a result, a specific fragment of about 0.8 kb was amplified in a combination of primer N1 and primer 4A. This fragment was cloned into pCR2.1-TOPO (pCR2.1-2) using a TOPO TA cloning kit (Invitrogen).

DNA sequence analysis was carried out using dRhodamine Terminator cycle sequencing ready reaction (Applied Biosystems) and ABI PRISM 310 genetic analyzer (Applied Biosystems). Decoding of the PCR product cloned in pCR2.1-2 revealed that this fragment was the amplification of the region from position 88 to position 812 of the sequence of SEQ ID NO: 1.

3b) Southern Analysis and Sequence Decoding Using Inverse PCR

In Southern analysis, a genomic DNA digested with EcoRI was subjected to agarose gel electrophoresis and then to blotting onto Hibond N+ (Amersham Biosciences). An ECF Random-Prime Labelling and Detection System (Amersham Biosciences) was used for hybridization and a Molecular Imager FX (Bio-Rad) was used for band detection.

A band of about 2 kb was detected when the PCR product obtained in 3a) in Example 3 was used as a probe.

Next, the genomic DNA was digested with EcoRI, and a fragment of about 2 kb was recovered and circularized using a DNA ligation kit ver. 2 (Takara Shuzo Co., Ltd.). Using the resulting loop as a template, the fragment was amplified using LA Taq (Takara Shuzo Co., Ltd.) with the following primers for inverse PCR by repeating 25 cycles of a serial step consisting of 30 seconds at 94° C., 30 seconds at 50° C., and 4.5 minutes at 72° C., after heat denaturation at 94° C. for 1 minute. This amplified fragment of about 2 kb was cloned using a TOPO TA cloning kit (Invitrogen) and its sequence was analyzed using primer walking.

Primer 1 for inverse PCR: TGACGCTGATACCAACGGCG (SEQ ID NO: 18) Primer 2 for inverse PCR: CTAGTGGCAGTATTGGACAG (SEQ ID NO: 19)

3c) Determination of Translation Region Using 3′ RACE and 5′ RACE Methods

The translation region was determined by the 3′ RACE and 5′ RACE methods using cDNA as a template. cDNA was prepared as follows.

As described in Example 1, a one ml portion of the culture of Neocosmospora vasinfecta var. vasinfecta PF1225 (FERM BP-7475) cultured in a TS medium was inoculated into 100 ml of an MY medium supplemented with 1% soybean saponin dispensed into a 500-ml Erlenmeyer flask. After incubation at 25° C. for 32 hours with shaking, cells were filtered through a nylon mesh (50 μm) and the cells thus obtained were frozen with liquid nitrogen. The frozen cells were smashed with a mortar and pestle and the whole RNA was extracted from the smashed cells. The whole RNA was extracted using ISOGEN (Nippon Gene) according to the attached protocol. mRNA was purified from the whole RNA using Oligotex-dT30 <Super> (Roche Diagnostics) according to the attached protocol.

By applying a 5′/3′ RACE kit (Roche Diagnostics) to this mRNA, 3′ and 5′ regions were amplified using 3′ RACE and 5′ RACE according to the attached protocol. In this case, in the 3′ RACE method, AmpriTaq Gold (Applied Biosystems) was used in the primary PCR and PCR Supermix High Fidelity (Lifetech Oriental Co., Ltd.) was used in the secondary PCR. In the primary and secondary PCRs in the 5′ RACE method, PCR Supermix High Fidelity (Lifetech Oriental Co., Ltd.) was used.

The sequences of 3′ RACE- and 5′ RACE-specific primers were as follows.

3′ RACE specific primer for primary PCR:

CCCAGGCCTTTAAGGATGGC (SEQ ID NO: 20) 3′ RACE specific primer for secondary PCR:

CTAGTGGCAGTATTGGACAG (SEQ ID NO: 19) 5′ RACE specific primer for cDNA synthesis:

TGACGCTGATACCAACGGCG (SEQ ID NO: 18) 5′ RACE specific primer for primary PCR:

CTGCTTGAGGGTAATGGGCTC (SEQ ID NO: 21) 5′ RACE specific primer for secondary PCR:

ACAGACGCCGGAGGAGAAGCG (SEQ ID NO: 22)

The translation region of the SDN gene shown in SEQ ID NO: 1 was thus determined. From the result in Example 2a), the N terminal of the mature protein of SDN amino acid sequence was found to be located at position 27 from Met of the translation initiation site.

The presence of introns in the translation region was confirmed by comparing DNA sequences of the genomic DNA and cDNA. It was revealed that no intron was present in this translation region.

Example 4 Expression of Saponin-Decomposing Enzyme (SDN) in Escherichia coli

PCR was carried out with primers for expression in E. coli shown below using the cDNA obtained in Example 3 as a template.

The translation region of the SDN gene was amplified using PCR Supermix High Fidelity (Lifetech Oriental Co., Ltd.) by repeating 25 cycles of a serial step consisting of 30 seconds at 94 C, 30 seconds at 50 C, and 2 minutes at 72 C, after denaturation at 94° C. for 1 minute. A fragment obtained by digesting the resulting product with restriction enzymes NdeI and BamHI was ligated to plasmid pET15b (Novagen, Inc.) digested with the same restriction enzymes, using a DNA ligation kit ver. 2 (Takara Shuzo Co., Ltd.). E. coli strain BL21 (DE3) was transformed using this product according to an ordinary method and colonies having ampicillin resistance were obtained.

N-terminal primer for E. coli expression:

GGGCATATGGCTTCTCCTCCTGCTTCTG (SEQ ID NO: 23) C-terminal primer for E. coli expression:

GGGGGATCCTTAAGTGCCGCTCTGAGGACTACG (SEQ ID NO: 24)

Colonies obtained were used for the following experiment.

Cells taken from the colonies were inoculated into 50 ml of an LB medium containing 50 μg/ml ampicillin dispensed in a 250-ml Erlenmeyer flask and incubation was carried out at 37° C. overnight with shaking. A 2 ml portion of this culture was further inoculated into 50 ml of an LB medium containing 50 μg/ml ampicillin dispensed in a 250-ml Erlenmeyer flask and incubation was carried out at 37° C. for 3 hours with shaking. Isopropyl-β-D-thiogalactopyranoside was added to the resulting culture at a final concentration of 0.4 mM and incubation was carried out for 3 hours for induction.

Cells thus cultured were collected by centrifugation and suspended in a buffer solution F (50 mM Tris-HCl buffer, 2 mM EDTA (pH 8.0)), after which cells were again recovered by centrifugation. After freezing at −80° C., these cells were suspended in 5 ml of a buffer solution F, lysozyme and Triton X 100 were added at final concentrations of 100 μg/ml and 0.1%, respectively, and the resulting suspension was allowed to stand at room temperature for about 20 minutes. Under ice cold, the cells were disrupted by ultrasonic treatment twice at a 50% duty cycle for 30 seconds using Sonifier 450 (BRANSON) and cell debris were removed by centrifugation.

Saponin-decomposing activity was measured according to Test Example 1 for the cell extract thus obtained as a crude enzyme solution.

As a result, a spot of the decomposed product, soyasapogenol B, was observed on TLC only for the extract of the cells in which the translation region of the saponin-decomposing enzyme was cloned.

Example 5 Expression of Saponin-Decomposing Enzyme (SDN) in Trichoderma viride

5a) Construction of Vector for Transformation

PCR was carried out as described in Example 4 with primers for expression in Trichoderma shown below using the cDNA obtained in Example 3 as a template.

A fragment obtained by digesting the resulting PCR product with restriction enzymes SmaI and PstI was ligated to plasmid pCB1-M2 (see Example 5 of WO 98/11239) digested with StuI and PstI, using a DNA ligation kit ver. 2 (Takara Shuzo Co., Ltd). The product was digested with XbaI, dephosphorylated and then linked to an XbaI cassette of the pyr4 gene derived from Neurospora crassa to construct pCB-SBe (FIG. 1).

N-terminal primer for expression in Trichoderma:

GGGCCCGGGGCGCATCATGCACTTCTTTGACAAAGCGAC (SEQ ID NO: 25) C-terminal primer for expression in Trichoderma:

GGGCTGCAGTTAAGTGCCGCTCTGAGGACT (SEQ ID NO: 26)

The XbaI cassette of the pyr4 gene was constructed as follows.

pFB6 (Biochem. Biophys. Res. Commun., 112, 284–289, 1983) was first digested with BglII and then partially digested with HindIII to recover a fragment of about 1.9 kb. This fragment was ligated to pLITMJS28 (New England Biolabs) digested with BglII and HindIII. Next, the product was digested with BglII, blunted using a DNA blunting kit (Takara Shuzo Co., Ltd.), and then linked to a phosphorylated linker pXbaI (Takara Shuzo Co., Ltd.) to construct the XbaI cassette of the pyr4 gene.

5b) Acquisition of Uracyl-Requiring Strain Derived from Trichoderma viride

A spore suspension of Trichoderma viride MC300-1 (about 1.0×10⁹ CFU/ml) was exposed to 2 UV lights at a distance of 30 cm with gentle mixing. The suspension was spread on a selective medium and incubated at 28° C. for 7 days and then grown strains were selected.

A selective medium used was a minimum medium (0.2% potassium dihydrogenphosphate, 0.4% ammonium sulfate, 0.03% urea, 0.03% magnesium sulfate heptahydrate, 0.03% calcium chloride, 0.5% glucose, 2.5% agar, 0.01% trace elements (5 mg of ion sulfate heptahydrate, 1.56 mg of manganese sulfate heptahydrate, 1.4 mg of zinc sulfate heptahydrate, and 2.0 mg of cobalt chloride dissolved in 1 L of water) supplemented with 10 μg/ml uridine and 1.0 mg/ml 5-fluoroorotic acid.

5c) Transformation of Trichoderma viride and Detection of Saponin-Decomposing Activity of each Recombinant

Cells of the uracyl-requiring Trichoderma viride strain obtained in 5b) of Example 5 were inoculated into 50 ml of a cell forming medium (1.0% yeast extract, 1.0% molt extract, 2.0% polypeptone, 2.5% glucose, 0.1% potassium dihydrogenphosphate, 0.05% magnesium sulfate heptahydrate, (pH 7.0 before sterilization)) dispensed in a 200-ml Erlenmeyer flask and incubation was carried out at 28° C. for 2 days with shaking. Mycelia were recovered from the resultant culture by centrifugation. Next, protoplasts were prepared from the mycelia, after which a DNA solution of plasmid pCB-SBe was added to carry out transformation (see Example 7 of WO 98/11239).

Further, in regeneration of transformants, 0.5 M sucrose was added to the minimum medium. Grown colonies were again inoculated onto the minimum medium and colonies grown in the medium were recognized as transformants.

Plasmid pCB-SBe was introduced into the uracyl-requiring Trichoderma viride strain. As a result, 3 transformants per 1 μg of pCB-SBe were obtained. Each of the transformants, 25 strains, was cultured (see Example 1 of WO 98/11239) and the resultant culture supernatant was subjected to SDS-PAGE, on which a band showing a molecular weight of about 68 kDa was observed only for the transformants.

Saponin-decomposing activity was measured according to Test Example 1 for this culture supernatant. As a result, a spot of the decomposed product, soyasapogenol B, was observed on TLC. On the other hand, this spot was not observed for the parent strain, the uracyl-requiring Trichoderma viride.

5d) Purification of Recombinant Saponin-Decomposing Enzyme (Recombinant SDN), and Comparison of its Activity with Wild-Type Saponin-Decomposing Enzyme Derived from Neocosmospora vasinfecta var. vasinfecta PF1225 (Wild-Type SDN)

The culture obtained in 5c) of Example 5 (about 700 ml) was centrifuged (8,000 rpm, 30 minutes) to remove cell debris. Ammonium sulfate (64 g) was added to about 560 ml of the supernatant thus obtained and the resulting precipitate was removed by centrifugation (8,000 rpm, 30 minutes). Further, 74 g of ammonium sulfate were added to about 600 ml of the resultant supernatant and the resultant precipitate was recovered. To this precipitate were added 100 ml of 0.05 M Tris-HCl buffer (pH 7.5) and 16 g of ammonium sulfate and the admixture was subjected to hydrophobic chromatography using Butyl Toyopearl 650S (26 mm i.d.×330 mm) (Tosoh Co.). Elution was carried out with a concentration gradient from a buffer solution C to 50 mM Tris-HCl buffer (pH 7.5) and an unadsorbed fraction and a fraction eluted at an ammonium sulfate concentration from 1 M to 0.6 M were recovered.

Each of the fraction thus obtained was concentrated using Pellicon XL (cut-off molecular weight: 10,000) (Millipore). To about 8 ml of this concentrate were added 1.3 g of ammonium sulfate and 2 ml of 0.5 M sodium phosphate buffer (pH 5.8) and the admixture was subjected to hydrophobic chromatography using 6 ml of Resource PHE (Amersham Biosciences). Elution was carried out with a concentration gradient from a buffer solution B to 0.1 M sodium phosphate buffer (pH 5.8) and an unadsorbed fraction was recovered.

The fraction thus obtained was concentrated using Ultrafree 15 (cut-off molecular weight: 5,000) (Millipore). This concentrate was subjected to gel filtration chromatography using Superdex 200 pg (16 mm i.d.×600 mm) (Amersham Biosciences). Elution was carried out with a buffer solution G (50 mM sodium phosphate buffer, 0.15 M sodium chloride (pH 7.0)) and a fraction of a cut-off molecular weight of about 68,000 was recovered.

SDS-PAGE was carried out with this fraction and a single band with an estimated molecular weight of about 68 kDa was observed.

The optimum pH and the optimum temperature for the recombinant saponin-decomposing enzyme thus purified (occasionally referred to as “recombinant SDN” hereinafter) and the saponin-decomposing enzyme purified in Example 1 (occasionally referred to as “wild-type SDN” hereinafter) were measured according to Test Example 2.

In measuring the optimum pH, first, to 50 μl of a 2% saponin solution were added 20 μl each of 0.5 M individual buffer solutions (sodium acetate buffer (pH 4.5, pH 5.0, pH 5.8); sodium phosphate buffer (pH 5.0, pH 5.8, pH 7.0) and Tris-HCl buffer (pH 7.0, pH 8.0, pH 9.0)) and a diluted enzyme solution to make a total volume of 100 μl. Reaction was carried out at 37° C. for 30 minutes, and then the amount of soyasapogenol B produced was measured.

Results are shown in FIG. 2.

In measuring the optimum temperature, first, to 50 μl of a 2% saponin solution were added 20 μl of 0.5 M sodium phosphate buffer (pH 5.8) and a diluted enzyme solution to make a total volume of 100 μl. Reaction was carried out at each specified temperature for 30 minutes, and then the amount of soyasapogenol B produced was measured.

Results are shown in FIG. 3.

As evident from these results, there was not much difference in activity although there was some difference in the molecular weight determined by SDS-PAGE.

Example 6 Amino Acid Sequence Analysis for Saponin-Decomposing Enzyme Derived from Aspergillus sp. PF1224 (SDA)

Saponin-decomposing enzyme purified from Aspergillus sp. PF1224 (FERM BP-8004) (SDA) (Reference Example 1) was fragmented as described in 2b) of Example 2 after excising a band of about 90 kDa, and subjected to HPLC as described in 2b) in Example 2 to fractionate the following 4 kinds of peptides.

Trp23.67: LYNPDSPQPISAK (SEQ ID NO: 27) Trp24.0: LQFNPAPK (SEQ ID NO: 28) Trp38.05: VDWFSDLTSTGQVTGSK (SEQ ID NO: 29) Trp24.5: GEVSGSASVSIIHD (SEQ ID NO: 30)

Example 7 Cloning and Sequence Analysis of SDA Gene

7a) Preparation of Long Probe Using PCR

A genomic DNA was isolated from cells cultured as described in Reference Example 1, as described in Example 3.

Based on the peptide sequences obtained in Example 6, the following oligonucleotides encoding these sequences were synthesized and used as primers for PCR.

Primer 23.67s1: TAYAAYCCIGAYTCNCC (SEQ ID NO: 31) Primer 23.67s2: TAYAAYCCNGAYAGYCC (SEQ ID NO: 32) Primer 24.0s: CARTTYAAYCCIGCNCC (SEQ ID NO: 33) Primer 24.0a: GGIGCNGGRTTRAAYTG (SEQ ID NO: 34) Primer 38.05a1: AARTCNGARAACCARTC (SEQ ID NO: 35) Primer 38.05a2: AARTCRCTRAACCARTC (SEQ ID NO: 36)

The PCR was carried out as described in 3a) in Example 3.

As a result, a fragment of about 1 kb was specifically amplified in a combination of primer 24.0s and primer 38.05a1 among the primers above, which was then cloned into pCR2.1-TOPO using a TOPO TA cloning kit (Invitrogen) (pSDAPCR1).

Results of sequence analysis revealed that the fragment cloned into pSDAPCR1 was the amplification of the region from position 709 to position 1748 of the sequence of SEQ ID NO: 3.

7b) Southern Analysis and Screening Using E. coli Colony Library

In Southern analysis, a genomic DNA previously digested with BamHI, EcoRI, and HindIII was subjected to agarose gel electrophoresis and then to blotting onto Hibond N+ (Amersham Bioscience). An ECF Random-Prime Labelling and Detection System (Amersham Bioscience) was used for hybridization and a Molecular Imager FX (Bio-Rad) was used for band detection.

Bands for a BamHI fragment of about 10 kb, an EcoRI fragment of about 20 kb, and a HindIII fragment of about 5 kb were detected when the PCR products obtained in 7a) above were used as a probe.

Next, the genomic DNA was digested with HindIII, and fragments of about 4 kb to 6 kb were recovered. The product was then linked to pUC18, which was previously digested with HindIII and dephosphorylated, to transform an E. coli strain DH5α. This E. coli was grown on an LB agar medium supplemented with ampicillin for colony formation, about 1,000 colonies thus obtained were blotted onto Hibond N+ (Amersham Bioscience). Here, one kind of positive clone (pSDAHind5/18) was obtained using the PCR product obtained in the abovementioned 7a) as a probe. This clone contained a HindIII fragment of about 5 kb.

7c) Determination of Translation Region Using 3′ RACE and 5′ RACE Methods

As described in 3c) in Example 3, the whole RNA was extracted from culture cells of Aspergillus sp. PF1224 (FERM BP-8004) prepared in Reference Example 1 and further, mRNA was isolated using a QuickPrep mRNA purification kit (Amersham Bioscience) according to the attached protocol.

By applying a 5′/3′ RACE kit (Roche Diagnostics) to this mRNA, 3′ and 5′ regions were amplified. LA Taq (Takara Shuzo Co., Ltd.) was used for each PCR.

Sequences of 3′ RACE- and 5′ RACE-specific primers were as follows.

3′ RACE specific primer for primary PCR:

CCTCGATACCCGAGGGACCG (SEQ ID NO: 37) 3′ RACE specific primer for secondary PCR:

GATGGGTTGCATGTTATCGC (SEQ ID NO: 38) 5′ RACE specific primer for cDNA synthesis:

GCGATAACATGCAACCCATC (SEQ ID NO: 39) 5′ RACE specific primer for primary PCR:

GACCACCTGGTTCAGTGGTG (SEQ ID NO: 40) 5′ RACE specific primer for secondary PCR:

GGGTTATAGAGTCTGGTAACG (SEQ ID NO: 41)

The translation region of the SDA gene shown in SEQ ID NO: 3 was thus determined. The SDA protein purified as Reference Example 1 was analyzed for the mature N-terminal amino acid sequence in the same manner as described in Example 2a). As a result, the N terminal of the mature protein of SDA amino acid sequence was found to be located at position 29 from Met of the translation initiation site. Further, the presence of introns in the translation region was confirmed by comparing DNA sequences of the genomic DNA and cDNA. It was revealed that no intron was present in this translation region.

Example 8 Expression of Saponin-Decomposing Enzyme Derived from Aspergillus sp. PF1224 (SDA) in Trichoderma viride

8a) Construction of Vector for Transformation

First, PCR was carried out as described in Example 4 with primers for expression in Trichoderma shown below using pSDAHind5/18 obtained in Example 7b as a template.

A fragment obtained by digesting the resulting PCR product with restriction enzymes StuI and XhoI was ligated to plasmid pCB1-M2 (see Example 5 of WO 98/11239) previously digested with StuI and XhoI using a DNA ligation kit ver. 2 (Takara Shuzo Co., Ltd.) to construct pCB-SDAe (FIG. 4).

N-terminal primer for SDA expression in Trichoderma:

GGGAGGCCTGCGCATCATGCATGTTGTCGCAAGTACCAC (SEQ ID NO: 42) C-terminal primer for SDA expression in Trichoderma:

GGGCTCGAGTACCTCAAGTCCCATTTGCCGGCTGC (SEQ ID NO: 43)

8b) Transformation of Trichoderma viride and Detection of Saponin-Decomposing Activity of each Recombinant

A host, the uracyl-requiring Trichoderma viride strain obtained in 5b) in Example 5, was transformed by the co-transformation method using pCB-SDAe and vector pPYR4 in which the pyr4 cassette was ligated to pLITMUS28 (see 5a) in Example 5), as described in 5c) in Example 5. As a result, about 12 strains of transformants per 1 μg of DNA were obtained.

Each of the transformants thus obtained was cultured (see Example 1 of WO 98/11239) and the resultant culture supernatant was subjected to SDS-PAGE, on which a band showing a molecular weight of about 80 kDa was observed only for the transformants.

Saponin-decomposing activity was measured using this culture supernatant as described in Test Example 1. As a result, a spot of the decomposed product, soyasapogenol B, was observed on TLC.

8c) Purification of Recombinant Saponin-Decomposing Enzyme Derived from Aspergillus sp. PF1224 (Recombinant SDA), and Comparison of its Activity with Wild-Type Saponin-Decomposing Enzyme Derived from Aspergillus sp. PF1224 (Wild-Type SDA)

The culture obtained in 8b) above (about 600 ml) was centrifuged (8,000 rpm, 30 minutes) to remove cell debris. Ammonium sulfate (57 g) was added to about 500 ml of the supernatant thus obtained and the resulting precipitate was removed by centrifugation. Further, 64 g (40% saturation fraction) and then 70 g (60% saturation fraction) of ammonium sulfate were added to this supernatant and the resultant precipitate was dissolved in a 0.1 M sodium phosphate buffer solution (pH 5.8). To the 60% saturation fraction was added ammonium sulfate to make a final concentration of 1M, and then the admixture was subjected to hydrophobic chromatography using Butyl Toyopearl 650S (26 mm i.d.×250 mm) (Tosoh Co.). Elution was carried out with a concentration gradient from a buffer solution A to a 0.1 M sodium phosphate buffer solution (pH 5.8) and a fraction eluted at an ammonium sulfate concentration from 0.9 M to 0.2 M was recovered.

The fraction thus obtained was concentrated using Pellicon XL (cut-off molecular weight: 10,000) (Millipore) and Ultrafree 15 (cut-off molecular weight: 10,000) (Millipore), desalted using a PD-10 column (Amersham Bioscience) and then subjected to ion-exchange chromatography using 6 ml of Resource Q (Amersham Bioscience). Elution was carried out with a concentration gradient from 50 mM Tris-HCl buffer (pH 7.5) to 50 mM Tris-HCl buffer-0.5 M sodium chloride (pH 7.5), and an unadsorbed fraction and a fraction eluted at a salt concentration of 0.08 M were recovered.

The fraction thus obtained was concentrated using Ultrafree 15 (cut-off molecular weight: 10,000) (Millipore) and then subjected to gel filtration chromatography using Superdex 200 pg (16 mm i.d.×600 mm) (Amersham Bioscience). Elution was carried out with a buffer solution G and a fraction of a cut-off molecular weight of about 50 kDa was recovered.

SDS-PAGE was carried out with this fraction and a single band with an estimated molecular weight of about 80 kDa was observed. Further, the cut-off molecular weight on the gel filtration and the molecular weight on the SDS-PAGE were different probably because this protein was adsorbed unspecifically to the carriers.

The optimum pH and the optimum temperature were measured for the recombinant SDA thus purified and the saponin-decomposing enzyme purified in Reference Example 1 (wild-type SDA), according to Test Example 2.

The optimum pH and the optimum temperature were measured as described in 5d) in Example 5.

Results are shown in FIGS. 5 and 6.

As a result, it was revealed that although the recombinant SDA exhibited lower specific activity in sodium phosphate buffer at pH 7 as compared to the wild-type SDA, it exhibited improved specific activity in Tris-HCl buffer and at high pHs.

Example 9 Isolation and Purification of Saponin-Decomposing Enzyme Derived from Eupenicillium brefeldianum PF1226 (SDE)

A PDA slant (about 1 cm²) of Eupenicillium brefeldianum PF1226 (FERM BP-7476) was inoculated into 100 ml of a TS medium dispensed into a 500-ml Erlenmeyer flask and then incubation was carried out at 25° C. for 3 days with shaking. The resulting culture (4 ml) was inoculated into 100 ml of an MY medium supplemented with 1.0% soybean saponin (Koshiro Seiyaku) dispensed into a 500-ml Erlenmeyer flask and then incubation was carried out for 7 days with shaking.

The resulting culture (about 1,000 ml) was filtered with a glass filter (G3) to remove cell debris. Ammonium sulfate (73 g) was added to this culture supernatant (about 640 ml) and the resulting precipitate was removed by centrifugation (8,000 rpm, 30 minutes). Further, ammonium sulfate (256 g) was added to the resulting supernatant (about 670 ml) and the resulting precipitate was recovered by centrifugation. This precipitate was dissolved in about 50 ml of 0.1 M sodium acetate buffer (pH 5.8), 13.2 g of ammonium sulfate was added, and then water was added to make a final concentration of 1 M ammonium sulfate-0.1M sodium acetate buffer.

After centrifugation, this solution was subjected to hydrophobic chromatography using Butyl Toyopearl 650S (26 mm i.d.×330 mm) (Tosoh Co.). Elution was carried out with a concentration gradient from a buffer solution C to 50 mM Tris-HCl buffer and a fraction eluted at an ammonium sulfate concentration of 0.7 M to 0.5 M was recovered.

The recovered fraction was concentrated using Pellicon XL (cut-off molecular weight: 10,000) (Millipore), after which sodium phosphate buffer and ammonium sulfate were added to make the concentrate having the same component as the buffer solution A and the resulting solution was subjected to hydrophobic chromatography using 6 ml of Resource PHE (Amersham Bioscience). Elution was carried out with a concentration gradient from a buffer solution A to a 0.1 M sodium phosphate buffer solution (pH 5.8) and a fraction eluted from an ammonium sulfate concentration of 1 M to 0.3 M was recovered.

This fraction was concentrated using Ultrafree 15 (cut-off molecular weight: 10,000) (Millipore), desalted using a PD-10 column (Amersham Bioscience) and then subjected to ion-exchange chromatography using 6 ml of Resource Q (Amersham Bioscience). Elution was carried out with a concentration gradient from 20 mM sodium phosphate buffer (pH 7.0) to 20 mM sodium phosphate buffer-1 M sodium chloride (pH 7.0), and an unadsorbed fraction was recovered.

The fraction thus obtained was concentrated using Ultrafree 15 (cut-off molecular weight: 10,000) (Millipore) and then subjected to gel filtration chromatography using Superdex 200 pg (16 mm i.d.×600 mm) (Amersham Bioscience). Elution was carried out with a buffer solution G and a fraction of a cut-off molecular weight of about 90 kDa was recovered.

SDS-PAGE was carried out with this fraction and a single band with an estimated molecular weight of about 90 kDa was observed.

Example 10 Analysis of Amino Acid Sequence of SDE

10a) Amino Acid Sequence of N-terminal Side

The N-terminal side amino acid sequence of the fraction prepared in Example 9 was analyzed as described in 2a) in Example 2. As a result, the following amino acid sequence was obtained.

N-terminal amino acid sequence: STTPAPPQPEPI (SEQ ID NO: 44)

10b) Peptide Mapping

The SDE purified in Example 9 was fragmented after excising a band of about 90 kDa, as described in 2b) in Example 2. The fragments were subjected to HPLC as described in 2b) in Example 2 and the following 3 kinds of peptides were fractionated.

Trp20.73: ADPAFSPDGTR (SEQ ID NO: 45) Trp34.21: LHPDDTHMGWSSF (SEQ ID NO: 46) Trp36.26: GFSGAGDEILYIGSTR (SEQ ID NO: 47)

Example 11 Cloning and Sequence Analysis of SDE Gene

11a) Preparation of Long Probes Using PCR

The genomic DNA was isolated from the cells cultured in Example 9, as described in Example 3.

Based on the sequences of the peptides obtained in Example 10, the following oligonucleotides encoding these sequences were synthesized and used as primers for PCR.

Primer Ns: CCICARCCNGARCCNAT (SEQ ID NO: 48) Primer 20.37a: CTRAAIGCNGGRTCNGC (SEQ ID NO: 49) Primer 34.21a: CCANCCCATRTGNGTRTC (SEQ ID NO: 50)

The PCR was carried out as described in 3a) in Example 3.

As a result, a fragment of about 1 kb was specifically amplified with a combination of primer Ns and primer 20.73a among the primers above. This fragment was cloned into pCR2.1-TOPO using a TOPO TA cloning kit (Invitrogen) (pSDEPCR5).

Results of sequence analysis revealed that the fragment cloned into pSDEPCR5 was the amplification of the region from position 70 to position 1247 of the sequence of SEQ ID NO: 5.

11b) Screening Using Southern Analysis and Phage Library

In Southern analysis, a genomic DNA digested with PstI, SphI and XhoI was subjected to agarose gel electrophoresis and then to blotting onto Hibond N+ (Amersham Bioscience). An ECF Random-Prime Labelling and Detection System (Amersham Bioscience) was used for hybridization and a Molecular Imager FX (Bio-Rad) was used for band detection.

Bands of a PstI fragment of about 3 kb, an SphI fragment of about 4 kb, and an XhoI fragment of about 6 kb were detected when the PCR product obtained in 11a) above was used as a probe.

Next, the genomic DNA was partially digested with Sau3A1. The resultant product was then linked to λEMBL3/BamHI vector (Stratagene) and packaged using a MaxPlax packaging extract kit (Epicentre Technologies). The resultant phage library (about 5×10⁴ PFU) was blotted onto Hibond N+ (Amersham Bioscience) and then 5 kinds of positive clones were obtained using the PCR fragment cloned in pSDEPCR5 as a probe, according to a DIG Hi-Prime DNA Labelling and Detection Kit (Roche Diagnostics). Of these clones, a XhoI fragment was recovered from a phage DNA containing the 6 kb XhoI fragment and cloned into pBluescript II KS+ (pSDEXho/IIKS+1).

The DNA sequence of the SDE translation region was determined as shown in SEQ ID NO: 5 by the transposon method using pSDEXho/IIKS+1 as a template.

As a result of Example 10a), the N terminal of the mature protein of SDE amino acid sequence was found to be located at position 18 from Met of the translation initiation site.

The presence of introns in the translation region was confirmed by comparing the sequences of the genomic DNA and cDNA. It was revealed that no intron was present in the translation region.

Example 12 Expression of Saponin-Decomposing Enzyme Derived from Eupenicillium brefeldianum PF1226 (SDE) in Trichoderma viride

12a) Construction of Vector for Transformation

PCR was carried out with primers for Trichoderma secretion shown below using pSDEXho/IIKS+1 obtained in Example 11 as a template, as described in Example 4.

A fragment obtained by digesting the resultant PCR product with restriction enzymes SmaI and XhoI was ligated to plasmid pCB1-M2 (see Example 5 of WO 98/11239) previously digested with SmaI and XhoI, using a DNA ligation kit ver. 2 (Takara Shuzo Co., Ltd) to construct pCB-SDEs (FIG. 7).

N-terminal primer for SDE secretion in Trichoderma:

GGGCCCGGGCTCAGACTACCCCGGCACCTCCTCAGCC (SEQ ID NO: 51) C-terminal primer for SDE secretion in Trichoderma:

GGGCTCGAGTACCTCATGCACCATTGAGCGGCTGGTGG (SEQ ID NO: 52)

12b) Transformation of Trichoderma viride and Detection of Saponin-Decomposing Activity of each Recombinant

Host cells of the uracyl-requiring Trichoderma viride strain obtained in 5b) of Example 5 were transformed by the co-transformation method using pCB-SDEs and vector pPYR4 in which the pyr4 cassette was linked to pLITMUS28 (see 5a) above), as described in 5c) in Example 5. As a result, about 28 strains of transformants per 1 μg of DNA were obtained.

Each of the transformants thus obtained was cultured (see Example 1 of WO 98/11239) and the resultant culture supernatant was subjected to SDS-PAGE, on which a band with an estimated molecular weight of about 67 kDa was observed only for the transformants.

Saponin-decomposing activity was measured as described in Test Example 1 for this culture supernatant. As a result, a spot of the decomposed product, soyasapogenol B, was observed on TLC.

12c) Purification of Recombinant Saponin-Decomposing Enzyme Derived from Eupenicillium brefeldianum PF 1226 (Recombinant SDE), and Comparison of its Activity with the Wild-Type Saponin-Decomposing Enzyme Derived from Eupenicillium brefeldianum PF1226 (Wild-Type SDE)

The culture obtained in 12b) in Example 12 (about 900 ml) was centrifuged (8,000 rpm, 30 minutes) to remove cell debris. Ammonium sulfate (78.7 g) was added to about 690 ml of the supernatant thus obtained and the resulting precipitate was removed by centrifugation. Further, 88.6 g of ammonium sulfate (40% saturation fraction) were added to the resultant supernatant and the resultant precipitate was dissolved to make 120 ml of 1 M ammonium sulfate-0.1 M sodium phosphate buffer (pH 5.8). A 20 ml portion of this solution was subjected to hydrophobic chromatography using Butyl Toyopearl 650S (26 mm i.d.×330 mm) (Tosoh Co.). Elution was carried out with a concentration gradient from a buffer solution A to a 0.1 M sodium phosphate buffer solution and a fraction eluted at an ammonium sulfate concentration from 0.2 M to 0 M was recovered.

The fraction thus obtained was concentrated using Pellicon XL (cut-off molecular weight: 10,000) (Millipore) and Ultrafree 15 (cut-off molecular weight: 5,000) (Millipore), desalted using a PD-10 column (Amersham Bioscience) and then subjected to ion-exchange chromatography using 6 ml of Resource Q (Amersham Bioscience). Elution was carried out with a concentration gradient from 50 mM Tris-HCl buffer (pH 7.5) to 50 mM Tris-HCl buffer-0.5 M sodium chloride (pH 7.5), and a fraction eluted at a salt concentration from 0 M to 0.1 M was recovered.

The fraction thus obtained was concentrated using Ultrafree 15 (cut-off molecular weight: 5,000) (Millipore) and then subjected to gel filtration chromatography using Superdex 200 pg (16 mm i.d.×600 mm) (Amersham Bioscience). Elution was carried out with a buffer solution G and a fraction of a cut-off molecular weight of about 50 kDa was recovered.

SDS-PAGE was carried out with this fraction and a single band with an estimated molecular weight of about 67 kDa was observed. Further, the cut-off molecular weight on the gel filtration and the molecular weight on the SDS-PAGE were different probably because this protein was adsorbed unspecifically to the carriers.

The optimum pH and the optimum temperature for the recombinant SDE thus purified and the saponin-decomposing enzyme purified in Example 9 (wild-type SDE) were measured according to Test Example 2.

The optimum pH and the optimum temperature were measured as described in 5d) in Example 5.

Results are shown in FIGS. 8 and 9.

As a result, it was revealed that the recombinant SDE exhibited improved activity in a Tris-HCl buffer solution and also at high pHs as compared to the wild-type SDE. 

1. An isolated polynucleotide encoding a protein selected from the group consisting of: (a) a protein comprising an amino acid sequence of SEQ ID NO: 4; and (b) a protein that has at least 95% homology to the protein comprising the amino acid sequence of SEQ ID NO: 4 and having saponin-decomposing activity.
 2. An isolated polynucleotide selected from the group consisting of: (i) a polynucleotide consisting of a DNA sequence of SEQ ID NO: 3; (ii) a polynucleotide that has at least 95% homology to the polynucleotide consisting of the DNA sequence of (i) and encodes a protein having saponin-decomposing activity; and (iii) a polynucleotide that hybridizes with a DNA sequence of a polynucleotide comprising the DNA sequence of (i) under stringent conditions and encodes a protein having saponin-decomposing activity, wherein said stringent conditions comprise a wash at 42° C. in 0.5% SSC, 0.4% SDS and 6M urea.
 3. The isolated polynucleotide according to claim 2, wherein the percent homology to the polynucleotide consisting of the DNA sequence of (i) is at least 98%.
 4. The isolated polynucleotide according to claim 1 or 2, which is derived from a filamentous fungus.
 5. The isolated polymicleotide according to claim 4, wherein said filamentous fungus belongs to the genus Aspergillus.
 6. The isolated polynucleotide according to claim 5, wherein said filamentous fungus belonging to the genus Aspergillus is Aspergillus sp. PF1224 (Accession No. FERM BP-8004) or a mutant thereof.
 7. A recombinant vector comprising the isolated polynucleotide of claim 1 or
 2. 8. An isolated host transformed with the recombinant vector of claim
 7. 9. The isolated host according to claim 8, wherein the host is a microorganism.
 10. The isolated host according to claim 9, wherein the host is a filamentous fungus.
 11. The isolated host according to claim 10, wherein said filamentous fungus belongs to the genus Trichoderma.
 12. The isolated host according to claim 11, wherein the host is Trichoderma viride strain MC300-1 (Accession No. FERM BP-6047) or a mutant thereof.
 13. The isolated host according to claim 8, which expresses a saponin-decomposing enzyme.
 14. A method for producing a protein of interest, which comprises culturing the isolated host of claim 8 and collecting the protein having saponin-decomposing activity from the resulting culture. 